Quality and Resolution Defined
July 6, 2011 3 Comments
During their careers, graphic designers will usually encounter clients and even coworkers that do not understand the graphic design world and common design concepts used in that world. One of the most common concepts that individuals find hard to grasp is the difference between raster files and vector files. This concept would be easier to understand if most of those individuals knew the definition of image resolution, which is usually confused with image quality. It is the job of the graphic designer to learn all of these concepts and to be able to explain these concepts to their coworkers and clients, when creating a project.
Image Quality and Image Resolution
Before understanding the differences or similarities between image quality and image resolution, a definition of each should be studied. First, we must understand how digital images are formed. When we take a photograph with a digital camera, or we create a new document using a raster-based software like Photoshop, we are creating digital images as raster files. These images are composed of pixels, or dots of color and digital information. When we talk about the Image Resolution of a digital image, we are referring to a number, a proportion, defined by the number of pixels that compose the image. When we talk about the Image Quality of a digital image, we are referring to the compression, the size of the file of the image, defined by the reduction or not of the information in each pixel within the image. This explains that image quality and image resolution are not exactly the same thing, but they both have to do with the pixels within a digital image.
More on Image Quality and Resolution
The number or proportion of pixels in an image determines the resolution of an image. This proportion is known as pixels per inch, or PPI, which can also be called dots per inch or DPI. This pixel per inch ratio or proportion refers to the number of pixels inside one square inch of the image. For example, images prepared for the web are usually saved with a 72 PPI resolution; therefore they have a low resolution. An image prepared to print is usually prepared at 300 PPI; therefore it has a high resolution. However, it is possible to have an image that has a high resolution of say 300 PPI, but is low quality. This can be accomplished by creating a 300 PPI image in Photoshop using the Image Size window, and then saving it as a JPG with a low quality of 1, or even 0. The same is true for creating an image that has a low resolution, like for example 72 PPI, and then save it with a high quality of 10, or even 12 on the image options of the saving window.
Do’s & Don’ts
As a graphic designer, you will most likely learn on your own the do’s and don’ts of image resolution and image quality throughout your career during trial and error. Nevertheless, there are several do’s and don’ts that you should be aware of when dealing with these concepts that I have learned on the job and will share with you.
- After manipulating an image in Photoshop, make sure to save as a copy and keep the original images intact.
- Always keep a Photoshop version (with layers) of your manipulated images, and a flattened JPG version.
- Remember you can go from high resolution to low resolution, but not the other way around. Therefore, always take and create high-resolution images.
- Always have a backup of your files.
- Never prepare an image for printing at less than 300 PPI.